High In "S" (Hold)
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 1994 Mazda MX-5 Miata, 1992 Mazda MX-5 Miata, 1992 Mazda MPV, 1992 Mazda B2200, and 1991 Mazda MX-5 Miata. However, it is still accessible from the selected car via links, so may be relevant.
Stuck pressure modifier valve. No variations when vacuum applied, missing diaphragm rod.